Bottom Line:
These results suggest that phosphorylation of tau by GSK-3beta promotes formation of tangle-like filament morphology.Although the severity of dementia has been found to correlate with the presence of NFTs, there is some question as to the identity of the neurotoxic agents involved.This model system will be beneficial in identifying intermediates or side reaction products that might be neurotoxic.

Background: Neurofibrillary tangles (NFTs) are intraneuronal aggregates associated with several neurodegenerative diseases including Alzheimer's disease. These abnormal accumulations are primarily comprised of fibrils of the microtubule-associated protein tau. During the progression of NFT formation, disperse and non-interacting tau fibrils become stable aggregates of tightly packed and intertwined filaments. Although the molecular mechanisms responsible for the conversion of disperse tau filaments into tangles of filaments are not known, it is believed that some of the associated changes in tau observed in Alzheimer's disease, such as phosphorylation, truncation, ubiquitination, glycosylation or nitration, may play a role.

Results: We have investigated the effects of tau phosphorylation by glycogen synthase kinase-3beta (GSK-3beta) on tau filaments in an in vitro model system. We have found that phosphorylation by GSK-3beta is sufficient to cause tau filaments to coalesce into tangle-like aggregates similar to those isolated from Alzheimer's disease brain.

Conclusion: These results suggest that phosphorylation of tau by GSK-3beta promotes formation of tangle-like filament morphology. The in vitro cell-free experiments described here provide a new model system to study mechanisms of NFT development. Although the severity of dementia has been found to correlate with the presence of NFTs, there is some question as to the identity of the neurotoxic agents involved. This model system will be beneficial in identifying intermediates or side reaction products that might be neurotoxic.

Mentions:
Polymerization samples of phosphorylated tau (induced with 25 μM ARA) were taken from the 20 h time point in the kinetic analysis described above and prepared for TEM. The filaments produced in the GSK-3β phosphorylated tau reactions were not distributed uniformly on the TEM grid, but clustered together into discrete aggregates (Figure 4A, C, and 4E). At higher magnifications (Figure 4B, D, and 4F), some filaments, although appearing to be a part of the aggregate, were not touching (Figure 4, white arrowheads); others seemed to be intertwined. Additional configurations appeared to represent branching filaments (Figure 4, white asterisk) as well as tendril-like fibers bridging the lateral gap between larger adjacent filaments (Figure 4, black arrowheads). The filaments within the aggregates had an average width of 16 ± 4 nm, similar to non-aggregated filaments seen in Figure 4, and to filaments formed from non-phosphorylated tau (Figure 5A and 5B).

Mentions:
Polymerization samples of phosphorylated tau (induced with 25 μM ARA) were taken from the 20 h time point in the kinetic analysis described above and prepared for TEM. The filaments produced in the GSK-3β phosphorylated tau reactions were not distributed uniformly on the TEM grid, but clustered together into discrete aggregates (Figure 4A, C, and 4E). At higher magnifications (Figure 4B, D, and 4F), some filaments, although appearing to be a part of the aggregate, were not touching (Figure 4, white arrowheads); others seemed to be intertwined. Additional configurations appeared to represent branching filaments (Figure 4, white asterisk) as well as tendril-like fibers bridging the lateral gap between larger adjacent filaments (Figure 4, black arrowheads). The filaments within the aggregates had an average width of 16 ± 4 nm, similar to non-aggregated filaments seen in Figure 4, and to filaments formed from non-phosphorylated tau (Figure 5A and 5B).

Bottom Line:
These results suggest that phosphorylation of tau by GSK-3beta promotes formation of tangle-like filament morphology.Although the severity of dementia has been found to correlate with the presence of NFTs, there is some question as to the identity of the neurotoxic agents involved.This model system will be beneficial in identifying intermediates or side reaction products that might be neurotoxic.

Background: Neurofibrillary tangles (NFTs) are intraneuronal aggregates associated with several neurodegenerative diseases including Alzheimer's disease. These abnormal accumulations are primarily comprised of fibrils of the microtubule-associated protein tau. During the progression of NFT formation, disperse and non-interacting tau fibrils become stable aggregates of tightly packed and intertwined filaments. Although the molecular mechanisms responsible for the conversion of disperse tau filaments into tangles of filaments are not known, it is believed that some of the associated changes in tau observed in Alzheimer's disease, such as phosphorylation, truncation, ubiquitination, glycosylation or nitration, may play a role.

Results: We have investigated the effects of tau phosphorylation by glycogen synthase kinase-3beta (GSK-3beta) on tau filaments in an in vitro model system. We have found that phosphorylation by GSK-3beta is sufficient to cause tau filaments to coalesce into tangle-like aggregates similar to those isolated from Alzheimer's disease brain.

Conclusion: These results suggest that phosphorylation of tau by GSK-3beta promotes formation of tangle-like filament morphology. The in vitro cell-free experiments described here provide a new model system to study mechanisms of NFT development. Although the severity of dementia has been found to correlate with the presence of NFTs, there is some question as to the identity of the neurotoxic agents involved. This model system will be beneficial in identifying intermediates or side reaction products that might be neurotoxic.